1,721,372 research outputs found
Risk assessment and mitigation at Copahue Volcano
No full text"Risk assessment" is a relatively new concept in Argentina, since the veryfirst hazard map was only recently constructed on the basis of the 1992 eruption of Copahue volcano (Patagonia). Copahue is considered a very active volcanic system since 13 eruptive events have been recognized overthe last 260 years. Most the events are phreatic and phreato-magmatic withVEI ≤ 2; nevertheless such eruptions represent a threat for thecommunities living in the surrounding areas of the emission centre, not only because of pyroclastic flows and tephra fall (the nearby villages,Caviahue and Copahue, have so far only experienced ash fallout), but also due to the possible formation of mud flows and flank collapse triggered by the volcanic activity. Owing to the frequent eruptions of Copahue, the most recent ones (2000, 2012) showed an increasing explosive character, hazard survey actions, such as thematic maps and contingency plans areconstantly, though slowly, modified. The risk assessment described in this chapter calls for the implementation of the monitoring network in the Argentina side of the volcano, since the only currently active seismic stations (OVDAS) are located in the Chilean side of the volcanic edifice, Copahue volcano lying at the border between the two countries.Moreover, the Chilean observatory adopts criteria of alert levels, which are distinctly different with respect to those of Argentina Civil Defense,producing misleading information to the population. The villages of Copahue and Caviahue are regarded as extremely vulnerable to possible future eruptions if larger magnitude events should occur. A review of the presently available potential hazard map, an improvement of people's education about the volcanic risks and a more interactive cooperation between the Chilean and Argentina scientific and administrative institutions are some of the immediate counter measures to be taken into account before a new explosive phase at Copahue.Fil: Caselli, Alberto Tomás. Universidad Nacional de Rio Negro. Sede Alto Valle. Laboratorio de Estudio y Seguimiento de Volcanes Activos.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Patagonia Norte. Instituto de Investigación en Paleobiología y Geología; ArgentinaFil: Liccioli, Caterina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Tassi, Franco. Università degli Studi di Firenze; Itali
Geochemistry of the magmatic-hydrothermal fluid reservoir of Copahue volcano (Argentina): insights from the chemical and isotopic features of fumarolic discharges
No full textThis study present the chemical (inorganic and organic) and isotopic compositions (d13C-CO2, d15N, 3He/4He, 40Ar/36Ar, d13C-CH4, dD-CH4, and dD-H2O and d18O-H2O) of gases from fluid discharges located at the foot of Copahue volcano. Gas samples were collected during 6 campaigns carried out from 1976 to 2012. Gas composition is typical of hydrothermal fluids from volcanic areas, since it consists of dominant CO2 and relatively high concentrations of H2S, H2, CH4 and N2. The isotopic ratios of He are the highest observed for a Southern American volcano to date (R/Ra up to 7.94). This feature is not common for gases from a classic arc-like setting, and is possibly related to an extensional regime subdued to asthenospheric thinning. The CO2/3He ratios (from 1.4 to 8.8×109) slightly exceeding that of MORB gases, and the d15N values (+5.3 to +5.5 ? vs. air) point to an occurrence of an additional crustal source for CO2 and N2. Gas discharges of the northern sector of the volcanic edifice are likely produced by mixing of hydrothermal gases with fluids from a shallow source permeating through local fault systems. Gas geothermometry based on chemical reactions characterized by slow kinetics, such as those involving the CO2-CH4 redox pair, are quenched at temperatures (~260 °C) and redox conditions [log(XH2/XH2O) = -2.8)] consistent with those measured in the goethermal wells. On the contrary, the C3H6-C3H8 pair, H2 and CO tend to re-adjust at decreasing temperatures and more oxidizing conditions [log(XH2/XH2O) ≤ -3.4] in the uprising vapor phase. The hydrothermal reservoir is mainly recharged by meteoric water whose isotopic signature is modified by water-rock interactions. The N2/He ratios measured in 2006-2007 were significantly lower than those of 2012, possibly due to variations of N2-bearing species in sediments interacting with the magmatic source. Considering that the R/Ra values of the 2006-2007 period were significantly higher than those measured in 2012, such compositional variation may also be explained by the injection of fresh N2and 3He-rich magma that triggered the 2000 eruption. This hypothesis, although speculative since no geochemical data of fumaroles are available from 1997 to 2006, implies that a geochemical monitoring of inert gas compounds discharged from the hydrothermal emissions could be used to detect the occurrence at depth of injections of new magma batches.Fil: Tassi, Franco. Università degli Studi di Firenze; ItaliaFil: Agusto, Mariano Roberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Estudios Andinos "Don Pablo Groeber". Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Estudios Andinos "Don Pablo Groeber"; ArgentinaFil: Vaselli, Orlando. Università degli Studi di Firenze; ItaliaFil: Chiodini, Giovanni. Istituto Nazionale di Geofisica e Vulcanologia; Itali
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Geochemistry of thermal fluids in NW Honduras: New perspectives for exploitation of geothermal areas in the southern Sula graben
No full textThe results of a geochemical survey on thermal waters and, for the first time for this site, gas discharges in five
geothermal sites (Azacualpa “La Cueva”, Río Ulua, Río Gualcarque, El Olivar and Laguna de Agua Caliente) in
NW Honduras are here presented and discussed. El Olivar and Laguna de Agua Caliente, in the southern part of
the Sula graben are very close to a Quaternary basaltic field, whereas Azacualpa “La Cueva”, Río Ulua and Río
Gualcarque, located to the southwest of the Yojoa Lake, direcly emerge from the Cretaceous limestone deposits.
The measured temperatures range between 37.5 and 104.8 °C. “Mature”, alkaline, Na-SO4 thermal waters
discharge from Azacualpa “La Cueva”, while those from El Olivar and Laguna de Agua Caliente are “immature”
and show a Na-HCO3 composition. Chemical equilibria of waters and gases from the Azacualpa “La Cueva”
thermal springs indicate temperatures ranging from 150 to 200 °C. Conversely, gas discharges from El Olivar
and Laguna de Agua Caliente have attained a partial chemical equilibrium in the liquid phase at slightly higher
temperatures (200–250 °C), although gas–gas faster reactions involving COseemto be adjusted in an isothermally
separated vapor phase. Unlike Azacualpa, SiO2 geothermometer at El Olivar and Laguna de Agua Caliente indicates
equilibrium temperatures for the liquid phase much lower than those calculated for the gas phase (≤120 °C).
We conclude that thermal waters from the Azacualpa area likely represent the direct emergence of a water
dominated reservoir having temperatures ≤150–200 °C. By contrast, at El Olivar and Laguna de Agua Caliente
hot springs are supplied by a boiling shallow aquifer fed by a vapor phase rising from a steam-dominated
zone. The above geochemical model is consistent with a geothermal reservoir hosted within the Cretaceous
carbonate sequences of the Yojoa Group in the whole investigated sites. The reservoir extensively crops out
in the Azacualpa area whereas the geothermal sites of the southern Sula graben (Laguna de Agua Caliente and
El Olivar) are covered by the Oligocene–Miocene volcano–sedimentary sequences of the Matagalpa formation,
possibly acting as efficient impermeable cap rocks.
These results significantly differ from those reported by previous studies and emphasize that the southern Sula
graben, in particular the El Olivar area, can represent among the investigated thermal springs, themost promising
site for the exploitation of a high-enthalpy geothermal field
Geothermal exploration in Central and Southern Sector of the Sula Graben (Honduras, Central America)
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